For the purpose of preventing the deterioration of the global environment and the exhaustion of oil resources, various techniques for ethanol production from plants or other biomass have been developed, and some are in practical use. For example, Patent Document 1 discloses a process for producing bioethanol, including fermenting a sugar solution, which has been prepared from biomass, into crude ethanol, and distilling the crude ethanol with vapor generated by burning the biomass, thereby obtaining anhydrous ethanol.
Biomass has already absorbed atmospheric CO2 during its generation. Therefore, bioethanol is entirely carbon neutral even if it emits CO2 into the atmosphere during combustion, and thus is expected to contribute to the prevention of global warming. In Japan, bioethanol is used in mixture with automotive gasoline. However, bioethanol emits a large amount of NOx into the exhaust gas and corrodes the automotive engine, so that the maximum rate of addition is limited to 3% by a law. Therefore, Bioethanol is not still effectively used.
In view of the above-described problems, the inventors considered that the conversion of bioethanol into other useful hydrocarbon would promote the utilization of biomass energy and contribute to the resolution of the global environmental problems. The inventors focused attention on the conversion of bioethanol into acetone, which is a ketone. Acetone is known to be converted into gasoline over a zeolite catalyst, and thus is useful for solving the above-described problems.
The Wacker process and the cumene process are generally used for industrial production of acetone. The Wacker process includes direct oxidation of propylene in air over a palladium chloride-copper chloride-based catalyst. The cumene process includes reaction between propylene and benzene over a catalyst of aluminum chloride or phosphoric acid, purifying cumene, and decomposing the cumene after oxidation to produce acetone and phenol. However, these processes use petroleum as a raw material, and thus will not contribute to the resolution of global environmental problems.
As described in Patent Document 1, biomass fermentation requires water, and biomass itself is normally hydrated. Therefore, bioethanol contains a large amount of water. However, the use of bioethanol as a fuel requires high purification. In addition, as shown in FIG. 5, the ethanol fractions in the vapor and liquid phases of ethanol-water mixture are almost the same in the region having a high ethanol concentration, so that a large amount of energy is necessary for increasing the ethanol concentration. According to the process described in Patent Document 1, hydrated ethanol is distilled using water vapor generated by burning biomass, thereby increasing the ethanol concentration. However, the process is still wasteful from the viewpoint of effective utilization of biomass energy. Furthermore, the water-acetone mixture produced according to the present invention has no azeotropic point different from a water-ethanol mixture, and thus allows easier acetone condensation in comparison with the water-ethanol mixture.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-208667